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WO2019186930A1 - Hot-stamped formed product - Google Patents

Hot-stamped formed product Download PDF

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Publication number
WO2019186930A1
WO2019186930A1 PCT/JP2018/013369 JP2018013369W WO2019186930A1 WO 2019186930 A1 WO2019186930 A1 WO 2019186930A1 JP 2018013369 W JP2018013369 W JP 2018013369W WO 2019186930 A1 WO2019186930 A1 WO 2019186930A1
Authority
WO
WIPO (PCT)
Prior art keywords
less
martensite
grain boundary
hot
hot stamping
Prior art date
Application number
PCT/JP2018/013369
Other languages
French (fr)
Japanese (ja)
Inventor
由梨 戸田
匹田　和夫
真吾 藤中
智仁 田中
Original Assignee
日本製鉄株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 日本製鉄株式会社 filed Critical 日本製鉄株式会社
Priority to JP2018535450A priority Critical patent/JP6477978B1/en
Priority to EP18912209.6A priority patent/EP3778951B1/en
Priority to CN201880088267.7A priority patent/CN111655885B/en
Priority to KR1020207027253A priority patent/KR102460598B1/en
Priority to MX2020010135A priority patent/MX2020010135A/en
Priority to PCT/JP2018/013369 priority patent/WO2019186930A1/en
Priority to US17/042,476 priority patent/US11180837B2/en
Publication of WO2019186930A1 publication Critical patent/WO2019186930A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component
    • Y10T428/12785—Group IIB metal-base component
    • Y10T428/12792—Zn-base component
    • Y10T428/12799—Next to Fe-base component [e.g., galvanized]

Definitions

  • the present invention relates to a hot stamping molded body having excellent bending deformability, particularly used for structural members and reinforcing members of automobiles and structures that require strength.
  • Hot stamping in which press forming is performed after heating a steel sheet to a high temperature in the austenite region, is being promoted.
  • Hot stamping has been attracting attention as a technology that achieves both molding on automobile members and ensuring strength, because quenching is performed in the mold simultaneously with pressing.
  • a molded body made of a high-strength steel plate using hot stamping must have the ability to absorb impact (collision deformation part) at the time of collision, and for that purpose, high impact absorption ability (bending deformation ability) is required.
  • Patent Document 1 as a technology that meets this requirement, hot stamping steel is annealed, and Mn and Cr are concentrated in the carbide to form a carbide that is difficult to dissolve. A technique for suppressing the growth of the material and making it finer is disclosed.
  • Patent Document 2 discloses a technique for refining austenite by heating at a heating rate of 90 ° C./s or less during hot stamping.
  • Patent Literature 3 Patent Literature 4, and Patent Literature 5 also disclose a technique for improving toughness by refining austenite.
  • Patent Documents 1 to 5 it is difficult to obtain finer austenite, and it is not possible to obtain strength or bending deformability higher than conventional.
  • the present invention has been made in view of the problems of the prior art, and aims to provide a hot stamp molded body that solves the above problems by securing a superior bending deformability in a hot stamp molded body of a high-strength steel sheet.
  • the present inventors diligently studied a method for solving the above problems.
  • the rotation angle is 5 ° to 75 ° among the grain boundaries whose rotation axis is the ⁇ 011> direction of the crystal grains of the lower bainite, martensite, and tempered martensite. It has been found that if 80% or more of the grain boundaries of 15 ° or more are generated, excellent bending deformability can be obtained.
  • the present invention has been made based on the above findings and has been further studied, and the gist thereof is as follows.
  • Component composition is mass%, C: 0.35% or more, 0.75% or less, Si: 0.005% or more, 0.25% or less, Mn: 0.5% or more, 3.0 %: Sol.Al: 0.0002% or more, 3.0% or less, Cr: 0.05% or more, 1.00% or less, B: 0.0005% or more, 0.010% or less, Nb: 0 0.01% or more, 0.15% or less, Mo: 0.005% or more, 1.00% or less, Ti: 0% or more, 0.15% or less, Ni: 0% or more, 3.00% or less, P : 0.10% or less, S: 0.10% or less, and N: 0.010% or less, the balance being Fe and inevitable impurities, the microstructure is lower bainite, martensite, and tempered martens The lower bainite, the martensite And with the ⁇ 011> direction of the crystal grains of the tempered martensite as the rotation axis, the grain boundary length at which the rotation angle is 15 °
  • the feature of the present invention is that, in the hot stamped molded body, the grain angle where the rotation angle is 5 ° or more and 75 ° or less with the ⁇ 011> direction of the crystal grains of lower bainite or martensite and tempered martensite as the rotation axis, By generating 80% or more of the grain boundaries having a rotation angle of 15 ° or more, excellent bending deformability is obtained.
  • the excellent bending deformability is improved because the large-angle boundary of 15 ° or more is more cracked than the small-angle boundary of less than 15 °. This is because the effect of suppressing propagation is high.
  • the present inventors have found that the above structure can be obtained by the following method.
  • the amount of molten steel cast per unit time is controlled. Thereby, precipitation of Mo and Nb is suppressed, and the solid solution amount of Mo and Nb in the steel is increased.
  • concentration of Mn and Cr in the carbide is suppressed by controlling the reduction ratio, temperature, and cooling conditions after rolling in hot finish rolling.
  • concentration of Mn and Cr in the carbide is suppressed by controlling the reduction ratio, temperature, and cooling conditions after rolling in hot finish rolling.
  • it is desirable that the carbide is easily dissolved. Therefore, it is important not to concentrate an element that inhibits dissolution of carbides such as Mn and Cr into carbides.
  • the strength of austenite can be increased due to the effects of solute Mo and Nb.
  • advantageous crystal orientations that relieve stress generated by the transformation are preferentially generated.
  • the ⁇ 112 ⁇ ⁇ 111> X-ray random intensity ratio of the crystal grains of the lower bainite, martensite and tempered martensite can be controlled in the hot stamping steel sheet.
  • the texture memory effect of austenite and martensite causes the lower bainite, martensite, and tempered martensite crystal grains to be formed.
  • the grain boundaries having a rotation angle of 5 ° to 75 ° with the ⁇ 011> direction as the rotation axis 80% or more of the grain boundaries having a rotation angle of 15 ° or more are generated.
  • the crystal orientation control expressed in the steel sheet for hot stamping is hot stamped by utilizing the grain boundaries of lower bainite, martensite, and tempered martensite as austenite reverse transformation sites. It can be handed over to the molded body.
  • % related to the component composition means mass%.
  • C 0.35% or more, 0.75% or less
  • C is an important element for obtaining a tensile strength of 2000 MPa or more. If it is less than 0.35%, martensite is soft and it is difficult to ensure a tensile strength of 2000 MPa or more, so C is 0.35% or more. Preferably it is 0.37% or more.
  • the upper limit is not particularly defined, the upper limit is set to 0.75% in view of the balance between required strength and early fracture suppression.
  • Si 0.005% or more, 0.25% or less
  • Si is an element that enhances the bending deformability and contributes to the improvement of the shock absorbing ability. If it is less than 0.005%, the bending deformability is poor and the impact absorbing ability deteriorates, so 0.005% or more is added. Preferably it is 0.01% or more. On the other hand, if it exceeds 0.25%, the amount of solid solution in the carbide increases and the carbide becomes difficult to dissolve, and the undissolved carbide becomes a reverse transformation site of austenite, and lower bainite, martensite or tempered martensite.
  • the grain boundary where the rotation angle is 15 ° or more cannot be controlled to 80% or more. Is 0.25%. Preferably it is 0.22% or less.
  • Mn 0.5% to 3.0%
  • Mn is an element that contributes to improvement in strength by solid solution strengthening. If it is less than 0.5%, the solid solution strengthening ability is poor and the martensite becomes soft, and it is difficult to ensure a tensile strength of 2000 MPa or more, so 0.5% or more is added. Preferably it is 0.7% or more.
  • the grain boundary having a rotation angle of 5 ° or more and 75 ° or less with the ⁇ 011> direction of the tempered martensite crystal grains as the rotation axis the grain boundary having a rotation angle of 15 ° or more cannot be controlled to 80% or more.
  • 3.0% is the upper limit. Preferably, it is 2.5% or less.
  • Al is an element that acts to deoxidize molten steel and to make the steel sound. If it is less than 0.0002%, deoxidation is sufficient and a coarse oxide is generated, causing premature breakage. Al is made 0.0002% or more. Preferably it is 0.0010% or more. On the other hand, if added over 3.0%, a coarse oxide is generated and causes early breakage, so the content is made 3.0% or less. Preferably it is 2.5% or less, More preferably, it is 0.5% or less.
  • Cr 0.05% or more, 1.00% or less
  • Cr is an element that contributes to improvement in strength by solid solution strengthening. If it is less than 0.05%, the solid solution strengthening ability is poor, the martensite becomes soft, and it is difficult to ensure a tensile strength of 2000 MPa or more, so 0.05% or more is added. Preferably it is 0.1% or more.
  • the grain boundary having a rotation angle of 5 ° or more and 75 ° or less with the ⁇ 011> direction of the tempered martensite crystal grains as the rotation axis the grain boundary having a rotation angle of 15 ° or more cannot be controlled to 80% or more.
  • the upper limit is 1.00%. Preferably, it is 0.8% or less.
  • B 0.0005% or more and 0.010% or less
  • B is an element that contributes to improving the strength by solid solution strengthening. If it is less than 0.0005%, the solid solution strengthening ability is poor and the martensite becomes soft, and it is difficult to ensure a tensile strength of 2000 MPa or more, so 0.0005% or more is added. Preferably it is 0.0008% or more.
  • the grain boundary having a rotation angle of 5 ° or more and 75 ° or less with the ⁇ 011> direction of the tempered martensite crystal grains as the rotation axis the grain boundary having a rotation angle of 15 ° or more cannot be controlled to 80% or more.
  • 0.010% is the upper limit. Preferably, it is 0.007% or less.
  • Nb 0.01% or more and 0.15% or less
  • Nb is an element that dissolves in the grain boundary of prior austenite and increases the strength of the grain boundary.
  • Nb improves the embrittlement strength of the grain boundary because it dissolves at the grain boundary and inhibits P grain boundary segregation. Therefore, 0.01% or more is added. Preferably it is 0.030% or more.
  • the ⁇ 112 ⁇ ⁇ 111> X-ray random strength of the crystal grains of lower bainite, martensite or tempered martensite The grain boundary where the ratio cannot be 2.8 or more, and as a result, the rotation angle is 5 ° or more and 75 ° or less with the ⁇ 011> direction of the crystal grains of lower bainite, martensite, or tempered martensite as the rotation axis.
  • the grain boundary where the rotation angle is 15 ° or more cannot be controlled to 80% or more, so it is 0.15% or less. Preferably it is 0.12% or less.
  • Mo 0.005% or more and 1.00% or less
  • Mo is an element that dissolves in the grain boundary of prior austenite and increases the strength of the grain boundary. Moreover, since Mo inhibits P grain boundary segregation by forming a solid solution at the grain boundary, the embrittlement strength of the grain boundary is improved. Therefore, 0.005 or more is added. Preferably it is 0.030% or more. On the other hand, when added over 1.00%, it becomes easy to precipitate as carbide, and it becomes easy to precipitate as carbide. In the steel sheet for hot stamping, ⁇ 112 ⁇ ⁇ of the grains of lower bainite, martensite or tempered martensite The X-ray random intensity ratio of 111> cannot be made 2.8 or more.
  • the rotation angle is 5 ° or more with the ⁇ 011> direction of the crystal grains of lower bainite, martensite, or tempered martensite as the rotation axis.
  • the grain boundaries that are 75 ° or less the grain boundaries that have a rotation angle of 15 ° or more cannot be controlled to 80% or more. Preferably it is 0.80% or less.
  • Ti 0% or more, 0.15% or less
  • Ti is not an essential element, but Ti is an element that contributes to improvement in strength by solid solution strengthening, and may be added as necessary.
  • it is preferable to set it as 0.01% or more.
  • it is 0.02% or more.
  • coarse carbides and nitrides are formed to cause early breakage, so the content is made 0.15% or less.
  • it is 0.12% or less.
  • Ni 0% or more and 3.00% or less
  • Ni is not an essential element, it is an element that contributes to improvement in strength by solid solution strengthening, and may be added as necessary.
  • it is preferable to set it as 0.01% or more.
  • it is 0.02% or more.
  • the steel becomes brittle and causes premature fracture, so the content is made 3.00% or less.
  • it is 2.00% or less.
  • P 0.10% or less
  • P is an impurity element and is an element that easily segregates at the grain boundary and lowers the embrittlement strength of the grain boundary. If it exceeds 0.10%, the embrittlement strength of the grain boundary is remarkably lowered and premature fracture is caused, so P is made 0.10% or less. Preferably it is 0.050% or less.
  • the lower limit is not particularly limited, but if it is reduced to less than 0.0001%, the de-P cost increases significantly and becomes economically disadvantageous, so 0.0001% is a practical lower limit on a practical steel sheet.
  • S is an impurity element and is an element that forms inclusions. If it exceeds 0.10%, inclusions are generated and cause early breakage, so S is made 0.10% or less. Preferably it is 0.0050% or less.
  • the lower limit is not particularly limited, but if it is reduced to less than 0.0015%, the de-S cost is significantly increased, which is economically disadvantageous, so 0.0015% is a practical lower limit on a practical steel sheet.
  • N 0.010% or less
  • N is an impurity element, and forms nitrides and causes early breakage. Therefore, the N content is set to 0.010% or less. Preferably it is 0.0075% or less.
  • the lower limit is not particularly limited, but if it is reduced to less than 0.0001%, the de-N cost greatly increases and becomes economically disadvantageous, so 0.0001% is a practical lower limit on a practical steel sheet.
  • the balance of the component composition is Fe and impurities.
  • impurities include elements that are allowed from steel raw materials or scraps and / or inevitably mixed in the steel making process, and are allowed to the extent that they do not impair the properties of the hot stamped article of the present invention.
  • Control of crystal orientation of lower bainite, martensite, and tempered martensite is an important structural factor for ensuring excellent bending deformability.
  • the ⁇ 011> direction of the crystal grains of the lower bainite, martensite, and tempered martensite is used as the rotation axis.
  • the grain boundaries having a rotation angle of 5 ° or more and 75 ° or less it is preferable to increase the grain boundaries having a rotation angle of 15 ° or more, and the ratio needs to be controlled to 80% or more. More preferably, it is 85% or more.
  • the ratio of the grain boundary where the rotation angle is 15 ° or more is Measure as follows.
  • a mirror surface is finished using a liquid in which a diamond powder having a particle size of 1 ⁇ m to 6 ⁇ m is dispersed in a diluent such as alcohol or pure water.
  • finish polishing is performed for 8 to 20 minutes using a standard colloidal silica suspension (particle size: 0.04 ⁇ m).
  • the polished sample is washed with acetone or ethyl alcohol, dried, and set in a scanning electron microscope.
  • the scanning electron microscope used is a model equipped with an EBSD detector (TSL DVC5 detector).
  • Crystal orientation information is obtained by EBSD measurement at a measurement interval of 0.1 ⁇ m in a range of 50 ⁇ m in the plate thickness direction and 50 ⁇ m in the rolling direction at the plate thickness 3/8 position to 5/8 position.
  • the measurement conditions are a vacuum level of 9.6 ⁇ 10 ⁇ 5 or less, an acceleration voltage of 15 kV, an irradiation current of 13 nA, a Binning size of 4 ⁇ 4, and an exposure time of 42 seconds.
  • the measurement data is among the grain boundaries of the body-centered cubic structure.
  • the length of the grain boundary whose rotation angle is 5 ° or more and 75 ° or less with the ⁇ 011> direction as the rotation axis is calculated.
  • the length of the grain boundary having a rotation angle of 15 ° to 75 ° with the ⁇ 011> direction as the rotation axis is calculated, and the rotation angle is 5 ° to 75 ° with the ⁇ 011> direction as the rotation axis.
  • the value divided by the grain boundary length is calculated.
  • Grain boundaries where the above measurement is carried out at least 5 locations and the average value is a grain boundary where the rotation angle is 5 ° or more and 75 ° or less with the ⁇ 011> direction of the crystal grains of lower bainite, martensite or tempered martensite as the rotation axis Of these, the ratio of grain boundaries where the rotation angle is 15 ° or more is used.
  • the microstructure In order for the hot stamping molded body to obtain a tensile strength of 1500 MPa or more, the microstructure needs to contain martensite or tempered martensite having an area ratio of 90% or more. Preferably it is 94% or more. From the viewpoint of securing tensile strength, the microstructure may be lower bainite.
  • the structure having an area ratio of 90% or more may be one of lower bainite, martensite, and tempered martensite, or a mixed structure thereof.
  • the balance of the microstructure is not particularly specified, and examples thereof include upper bainite, retained austenite, and pearlite.
  • the area ratio of lower bainite, martensite, and tempered martensite is measured as follows.
  • a section perpendicular to the plate surface is cut out from the center of the hot stamped body, and the measurement surface is polished using # 600 to # 1500 silicon carbide paper, and then a diamond powder having a particle size of 1 to 6 ⁇ m is diluted with a diluent such as alcohol or the like. Use a liquid dispersed in pure water to give a mirror finish.
  • the corroded sample is washed with acetone or ethyl alcohol, dried, and subjected to observation with a scanning electron microscope.
  • the scanning electron microscope used is assumed to be equipped with a two-electron detector.
  • the sample was irradiated with an electron beam at an acceleration voltage of 10 kV and an irradiation current level of 8, and the sample thickness was 1/8 to 3/8 centered on the 1/4 position.
  • a secondary electron image of the range is taken.
  • the photographing magnification is 10,000 times on the basis of a screen of 386 mm wide ⁇ 290 mm long, and the number of photographing fields is 10 fields or more.
  • the crystal grain boundary and the carbide are captured with a bright contrast, and therefore the structure can be easily determined by the position of the crystal grain boundary and the carbide.
  • carbide is formed inside the crystal grain, it is tempered martensite or lower bainite, and the structure where the carbide is not observed inside the crystal grain is martensite.
  • the structure in which carbides are formed at the grain boundaries is upper bainite or pearlite.
  • the same field of view as the position where the secondary electron image is taken is measured by an electron backscatter diffraction method.
  • the scanning electron microscope to be used is equipped with a camera capable of electron backscatter diffraction.
  • the sample In a vacuum of 9.6 ⁇ 10 ⁇ 5 or less, the sample is irradiated with an electron beam at an acceleration voltage of 25 kV and an irradiation current level of 16, and a face-centered cubic lattice map is created from the obtained measurement data.
  • the imaging magnification is to create a mesh of 2 ⁇ m intervals on a photograph taken at a magnification of 10,000 with reference to a screen of horizontal 386 mm ⁇ longitudinal 290 mm, and select a microstructure located at the intersection of the mesh.
  • a value obtained by dividing the number of intersections of each structure by all the intersections is defined as the area fraction of the microstructure. This operation is performed in 10 fields of view, and the average value is calculated as the area ratio of the microstructure.
  • the molten steel which has the above-mentioned chemical composition is made into a steel piece (slab) by a continuous casting method.
  • this continuous casting process it is preferable to set the molten steel casting amount per unit time to 6 ton / min or less.
  • the casting amount (casting speed) per unit time of molten steel exceeds 6 ton / min during continuous casting, microsegregation of Mn increases and the nucleation amount of precipitates mainly composed of Mo and Nb increases. . More preferably, the casting amount is 5 ton / min or less.
  • the lower limit of the casting amount is not particularly limited, but is preferably 0.1 ton / min or more from the viewpoint of operation cost.
  • Hot rolling process The above-mentioned steel slab is hot-rolled to obtain a steel plate. At that time, the hot rolling is finished in a temperature range defined by the formula (2) of A3 transformation temperature + 10 ° C. or more and A3 transformation temperature + 200 ° C. or less, and the final rolling reduction at that time is set to 12% or more. Cooling is started within 1 second after the completion, and the temperature range from the finish rolling finish temperature to 550 ° C. is cooled at a cooling rate of 100 ° C./second or more and wound at a temperature of less than 500 ° C.
  • A3 transformation temperature 850 + 10 ⁇ (C + N) ⁇ Mn + 350 ⁇ Nb + 250 ⁇ Ti + 40 ⁇ B + 10 ⁇ Cr + 100 ⁇ Mo (2)
  • the recrystallization of austenite is promoted by setting the finish rolling temperature to A3 transformation temperature + 10 ° C. or higher.
  • A3 transformation temperature + 10 ° C. or higher is suppressed, and the precipitation sites of Nb and Mo can be reduced.
  • the consumption of C can be suppressed by reducing the precipitation sites of Nb and Mo, the number density of carbides can be increased in a later step.
  • it is A3 transformation temperature + 30 ° C. or higher.
  • finish rolling temperature By setting the finish rolling temperature to A3 transformation temperature + 200 ° C. or less, excessive grain growth of austenite is suppressed.
  • finish rolling in a temperature range of A3 transformation temperature + 200 ° C. or less recrystallization of austenite is promoted, and excessive grain growth does not occur. Therefore, fine carbides can be obtained in the winding process.
  • it is A3 transformation temperature +150 degrees C or less.
  • Austenite recrystallization is promoted by setting the reduction ratio of finish rolling to 12% or more. Thereby, the formation of a low-angle grain boundary in the crystal grains is suppressed, and the precipitation sites of Nb and Mo can be reduced. Preferably, it is 15% or more.
  • Nb and Mo in austenite By starting cooling within 1 second after finishing rolling, preferably within 0.8 seconds, and cooling the temperature range from the finishing rolling finishing temperature to 550 ° C. at a cooling rate of 100 ° C./second or more, Nb and The residence time in the temperature range where the precipitation of Mn is promoted can be reduced. As a result, precipitation of Nb and Mo in austenite can be suppressed, and the amount of Nb and Mo dissolved in the austenite grain boundary increases.
  • the coiling temperature By setting the coiling temperature to less than 500 ° C., the above effect can be enhanced, and the ⁇ 112 ⁇ ⁇ 111> X-ray random intensity ratio of the crystal grains can be controlled in the hot stamping steel sheet.
  • Nb and Mo are dissolved in austenite.
  • austenite By transforming from austenite in which Nb and Mo are dissolved to lower bainite, martensite, or tempered martensite, Nb, Mo Produces a crystal orientation that is advantageous in order to relieve the stress generated by transformation, so that the ⁇ 112 ⁇ ⁇ 111> X-ray random intensity ratio of the crystal grains can be controlled.
  • it Preferably it is less than 480 degreeC.
  • the lower limit is not particularly defined, but it is difficult to wind up at room temperature or lower in actual operation, so the room temperature is the lower limit.
  • a plating layer may be formed on the surface of the softening layer for the purpose of improving corrosion resistance.
  • the plating layer may be either an electroplating layer or a hot dipping layer.
  • Examples of the electroplating layer include an electrogalvanizing layer and an electro Zn—Ni alloy plating layer.
  • the hot dip galvanized layer includes hot dip galvanized layer, alloyed hot dip galvanized layer, hot dip aluminum plated layer, hot dip Zn-Al alloy plated layer, hot dip Zn-Al-Mg alloy plated layer, hot dip Zn-Al-Mg-Si alloy.
  • a plating layer etc. are illustrated.
  • the adhesion amount of the plating layer is not particularly limited and may be a general adhesion amount.
  • the hot stamping molded body of the present invention is a hot stamping steel sheet which is heated and held at a temperature range of 500 ° C. or higher and A3 point or lower at an average heating rate of less than 100 ° C./s, and then hot stamped and molded.
  • the molded body is produced by cooling to room temperature.
  • a part or all of the hot stamping body may be tempered at a temperature of 200 ° C. or higher and 500 ° C. or lower.
  • the lower bainite, martensite, and tempered martensite grain boundaries formed in the steel sheet for hot stamping are heated to a temperature range of 500 ° C. or more and A3 or less at an average heating rate of less than 100 ° C./s. It functions as a transformation site, and the texture angle effect of austenite and martensite allows the rotation angle to be 5 ° to 75 ° with the ⁇ 011> direction of the crystal grains of the lower bainite, martensite, or tempered martensite as the rotation axis.
  • 80% or more of the grain boundaries that have a rotation angle of 15 ° or more can be generated.
  • the average heating rate is 100 ° C./s or more, fine carbides become austenite reverse transformation sites, so that the texture memory effect of austenite and martensite cannot be obtained.
  • it is 90 degrees C / s or less.
  • the lower limit is not particularly specified, but if it is less than 0.01 ° C./s, the production cost is disadvantageous, so 0.01 ° C./s or more is preferable. More preferably, it is 1 ° C./s or more.
  • the holding temperature at the time of hot stamping is preferably A3 point + 10 ° C. or higher and A3 point + 150 ° C. or lower in order to refine the prior austenite grains.
  • the cooling rate after hot stamping is preferably 10 ° C./s or more from the viewpoint of improving the strength.
  • the conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited.
  • the present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
  • Steel strips produced by casting molten steel having the composition shown in Tables 1-1 to 1-3 are subjected to hot rolling and cold rolling shown in Tables 2-1 to 2-3 to obtain hot stamping steel plates.
  • the steel sheet for hot stamping was subjected to the heat treatment shown in Tables 3-1 to 3-3, and hot stamping was performed to produce a molded body.
  • Tables 3-1 to 3-3 show the microstructure and mechanical properties of the hot stamping products.
  • the area ratio of the lower bainite, martensite, and tempered martensite, and the rotation angle of 5 as the rotation axis is the ⁇ 011> direction of the crystal grains of the lower bainite, martensite, or tempered martensite.
  • the ratio of the grain boundary where the rotation angle is 15 ° or more among the grain boundaries where the angle is from 75 ° to 75 ° was measured.
  • the strength of the hot stamped molded body was evaluated by a tensile test.
  • a tensile test a No. 5 test piece described in JIS Z 2201 was prepared, and the test was performed according to the test method described in JIS Z 2241.
  • the maximum strength was 2000 MPa or more.
  • the bending deformability was evaluated under the following measurement conditions based on the VDA standard (VDA238-100) defined by the German Automobile Manufacturers Association.
  • VDA238-100 the displacement at the maximum load obtained by a bending test is converted into an angle based on the VDA, the maximum bending angle is obtained, and a material having a maximum bending angle of 50 ° or more is regarded as acceptable.
  • the hot stamped article of the present invention has a tensile strength of 2000 MPa or more and was confirmed to have excellent bending deformability. On the other hand, in the example where the chemical composition and the manufacturing method are not appropriate, the target characteristics were not obtained.

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Abstract

This hot-stamped formed product for a high-strength steel sheet having excellent bending deformability is characterized in that: the steel sheet has a prescribed component composition; an area ratio of 90% or more in the microstructure of the steel sheet corresponds to lower bainite, martensite, and/or tempered martensite; and, with the <011> direction of the crystal grains of lower bainite, martensite, and tempered martensite taken as the axis of rotation, the ratio of the length of a grain boundary where the angle of rotation is 15° or higher to the length of a grain boundary where the angle of rotation is 5° to 75° is 80% or higher.

Description

ホットスタンプ成形体Hot stamping body

　本発明は、強度が必要な自動車や構造物の構造部材や補強部材に使用する、特に、優れた曲げ変形能を有するホットスタンプ成形体に関する。 The present invention relates to a hot stamping molded body having excellent bending deformability, particularly used for structural members and reinforcing members of automobiles and structures that require strength.

　近年、環境保護及び省資源化の観点から自動車車体の軽量化が求められており、そのため、自動車用部材への高強度鋼板の適用が加速している。しかし、鋼板の高強度化に伴い成形性は劣化するので、高強度鋼板においては、複雑な形状の部材への成形性が課題となる。 In recent years, the weight reduction of automobile bodies has been demanded from the viewpoint of environmental protection and resource saving, and for this reason, the application of high-strength steel sheets to automobile members is accelerating. However, since the formability deteriorates as the strength of the steel sheet increases, the formability of the high-strength steel sheet into a member having a complicated shape becomes a problem.

　このような課題を解決するため、鋼板をオーステナイト域の高温まで加熱した後にプレス成形を実施するホットスタンプの適用が進められている。ホットスタンプは、プレス加工と同時に、金型内において焼入れ処理を実施するので、自動車用部材への成形と強度確保を両立する技術として注目されている。 In order to solve such problems, the application of hot stamping, in which press forming is performed after heating a steel sheet to a high temperature in the austenite region, is being promoted. Hot stamping has been attracting attention as a technology that achieves both molding on automobile members and ensuring strength, because quenching is performed in the mold simultaneously with pressing.

　一方で、高強度鋼板をホットスタンプで成形した成形体には、衝突時に衝撃を吸収する性能（衝突変形部位）が必要であり、そのためには高い衝撃吸収能（曲げ変形能）が必要とされる。 On the other hand, a molded body made of a high-strength steel plate using hot stamping must have the ability to absorb impact (collision deformation part) at the time of collision, and for that purpose, high impact absorption ability (bending deformation ability) is required. The

　特許文献１には、この要求に応える技術として、ホットスタンプ用鋼鈑を焼鈍し、炭化物中にＭｎやＣｒを濃化させて溶解し難い炭化物とすることにより、ホットスタンプ加熱時にこれら炭化物によってオーステナイトの成長を抑制して細粒化させる技術が開示されている。 In Patent Document 1, as a technology that meets this requirement, hot stamping steel is annealed, and Mn and Cr are concentrated in the carbide to form a carbide that is difficult to dissolve. A technique for suppressing the growth of the material and making it finer is disclosed.

　特許文献２には、ホットスタンプ加熱時に９０℃／ｓ以下の加熱速度で昇温することにより、オーステナイトを細粒化させる技術が開示されている。 Patent Document 2 discloses a technique for refining austenite by heating at a heating rate of 90 ° C./s or less during hot stamping.

　特許文献３、特許文献４、特許文献５にもオーステナイトを細粒化させて靱性を向上させる技術が開示されている。 Patent Literature 3, Patent Literature 4, and Patent Literature 5 also disclose a technique for improving toughness by refining austenite.

国際公開第２０１５／１４７２１６号International Publication No. 2015/147216 特許第５３６９７１４号公報Japanese Patent No. 5369714 特許第５１１４６９１号公報Japanese Patent No. 5114691 特開２０１４－１５６３８号公報JP 2014-15638 A 特開２００２－３０９３４５号公報JP 2002-309345 A

　しかしながら、上記特許文献１～５に開示されている技術では、さらに細粒化されたオーステナイトを得ることは困難であり、従来以上の強度または曲げ変形能を得ることが望めない。 However, with the techniques disclosed in Patent Documents 1 to 5, it is difficult to obtain finer austenite, and it is not possible to obtain strength or bending deformability higher than conventional.

　本発明は、従来技術の課題に鑑み、高強度鋼板のホットスタンプ成形体において、より優れた曲げ変形能を確保することを課題とし、該課題を解決するホットスタンプ成形体を提供することを目的とする。 The present invention has been made in view of the problems of the prior art, and aims to provide a hot stamp molded body that solves the above problems by securing a superior bending deformability in a hot stamp molded body of a high-strength steel sheet. And

　本発明者らは上記課題を解決する方法について鋭意検討した。その結果、ホットスタンプ成形体において、下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を８０％以上生成させれば、優れた曲げ変形能が得られることを見出した。 The present inventors diligently studied a method for solving the above problems. As a result, in the hot stamped molded body, the rotation angle is 5 ° to 75 ° among the grain boundaries whose rotation axis is the <011> direction of the crystal grains of the lower bainite, martensite, and tempered martensite. It has been found that if 80% or more of the grain boundaries of 15 ° or more are generated, excellent bending deformability can be obtained.

　本願発明は上記の知見に基づき、さらに検討を進めてなされたものであって、その要旨は以下のとおりである。 The present invention has been made based on the above findings and has been further studied, and the gist thereof is as follows.

　（１）成分組成が、質量％で、Ｃ：０．３５％以上、０．７５％以下、Ｓｉ：０．００５％以上、０．２５％以下、Ｍｎ：０．５％以上、３．０％以下、sol.Ａｌ：０．０００２％以上、３．０％以下、Ｃｒ：０．０５％以上、１．００％以下、Ｂ：０．０００５％以上、０．０１０％以下、Ｎｂ：０．０１％以上、０．１５％以下、Ｍｏ：０．００５％以上、１．００％以下、Ｔｉ：０％以上、０．１５％以下、Ｎｉ：０％以上、３．００％以下、Ｐ：０．１０％以下、Ｓ：０．１０％以下、及びＮ：０．０１０％以下を含有し、残部がＦｅ及び不可避的不純物であり、ミクロ組織が、下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトの少なくとも１種を、面積率で９０％以上含み、上記下部ベイナイト、上記マルテンサイト、及び上記焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として、回転角が５°以上７５°以下となる粒界の長さに対する回転角が１５°以上となる粒界の長さの割合が８０％以上であることを特徴とするホットスタンプ成形体。 (1) Component composition is mass%, C: 0.35% or more, 0.75% or less, Si: 0.005% or more, 0.25% or less, Mn: 0.5% or more, 3.0 %: Sol.Al: 0.0002% or more, 3.0% or less, Cr: 0.05% or more, 1.00% or less, B: 0.0005% or more, 0.010% or less, Nb: 0 0.01% or more, 0.15% or less, Mo: 0.005% or more, 1.00% or less, Ti: 0% or more, 0.15% or less, Ni: 0% or more, 3.00% or less, P : 0.10% or less, S: 0.10% or less, and N: 0.010% or less, the balance being Fe and inevitable impurities, the microstructure is lower bainite, martensite, and tempered martens The lower bainite, the martensite And with the <011> direction of the crystal grains of the tempered martensite as the rotation axis, the grain boundary length at which the rotation angle is 15 ° or more with respect to the grain boundary length at which the rotation angle is 5 ° or more and 75 ° or less. A hot stamping molded product characterized in that the ratio is 80% or more.

　（２）めっき層を有することを特徴とする前記（１）のホットスタンプ成形体。 (2) The hot stamping molded product according to (1) above, which has a plating layer.

　本発明によれば、優れた曲げ変形能を有するホットスタンプ成形体を提供することができる。 According to the present invention, it is possible to provide a hot stamping body having excellent bending deformability.

　本発明の特徴は、ホットスタンプ成形体において、下部ベイナイト又はマルテンサイト及び焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として、回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を８０％以上生成させることにより、優れた曲げ変形能が得ることである。ホットスタンプ成形体の組織をこのような組織とすることにより、優れた曲げ変形能が向上するのは、１５°以上の大傾角粒界が、１５°未満の小傾角粒界よりも、亀裂の伝播を抑制する効果が高いためである。本発明者らは鋭意検討の結果、以下の方法により上記の組織が得られることを知見した。 The feature of the present invention is that, in the hot stamped molded body, the grain angle where the rotation angle is 5 ° or more and 75 ° or less with the <011> direction of the crystal grains of lower bainite or martensite and tempered martensite as the rotation axis, By generating 80% or more of the grain boundaries having a rotation angle of 15 ° or more, excellent bending deformability is obtained. By making the structure of the hot stamped molded body into such a structure, the excellent bending deformability is improved because the large-angle boundary of 15 ° or more is more cracked than the small-angle boundary of less than 15 °. This is because the effect of suppressing propagation is high. As a result of intensive studies, the present inventors have found that the above structure can be obtained by the following method.

　第一段階として、単位時間当たりの溶鋼の鋳込み量を制御する。これにより、Ｍｏ、Ｎｂの析出を抑制し、鋼中のＭｏ、Ｎｂの固溶量を増加させる。 As a first step, the amount of molten steel cast per unit time is controlled. Thereby, precipitation of Mo and Nb is suppressed, and the solid solution amount of Mo and Nb in the steel is increased.

　単位時間当たりの溶鋼の鋳込み量を制御してＭｏ、Ｎｂの析出を抑制すると、同時にＭｎのミクロ偏析も抑制されるため、Ｐのトラップサイトが消失し、仕上げ圧延時にＰが旧オーステナイト粒界に偏析する。すると、粒界の脆化強度が低下するので、結晶方位を制御しても、曲げ変形能が十分に得られない。これは、ＭｎとＰの親和性が高いために、Ｍｎの偏析がＰのトラップサイトとして機能しており、Ｍｎの偏析を解消することによりＰが旧オーステナイト粒界に拡散するためである。本発明では、圧延条件の制御によりこの課題を解決する。 When the amount of molten steel cast per unit time is controlled to suppress the precipitation of Mo and Nb, the micro segregation of Mn is also suppressed at the same time, so the P trap site disappears, and P becomes a prior austenite grain boundary during finish rolling. Segregate. Then, since the embrittlement strength of the grain boundary is lowered, even if the crystal orientation is controlled, sufficient bending deformability cannot be obtained. This is because the affinity between Mn and P is high, so that the segregation of Mn functions as a trap site for P, and P diffuses into the prior austenite grain boundaries by eliminating the segregation of Mn. In the present invention, this problem is solved by controlling the rolling conditions.

　第二段階として、熱間仕上げ圧延の圧下率、温度、圧延後の冷却条件を制御することにより、炭化物中へのＭｎやＣｒの濃化を抑制させる。下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトの結晶粒界を優先的なオーステナイトの逆変態サイトとするためには、炭化物が溶解し易いことが望ましい。そのため、ＭｎやＣｒ等の炭化物溶解を阻害する元素を炭化物に濃化させないことが重要である。 As the second stage, concentration of Mn and Cr in the carbide is suppressed by controlling the reduction ratio, temperature, and cooling conditions after rolling in hot finish rolling. In order to make the grain boundaries of lower bainite, martensite, and tempered martensite a preferential austenite reverse transformation site, it is desirable that the carbide is easily dissolved. Therefore, it is important not to concentrate an element that inhibits dissolution of carbides such as Mn and Cr into carbides.

　また、Ｍｏ、Ｎｂの析出を抑制させ、旧オーステナイトの粒界にＮｂやＭｏを固溶させることにより、Ｐの偏析サイトをＮｂとＭｏによって占有させることにより、旧オーステナイトへのＰの偏析を解消する。これにより、単にＭｏ又はＮｂによる粒界強度の向上のみならず、粒界の脆化強度の低減を抑制することができる。 In addition, by suppressing the precipitation of Mo and Nb and by dissolving Nb and Mo in the grain boundaries of the prior austenite, the segregation sites of P are occupied by Nb and Mo, thereby eliminating the segregation of P into the prior austenite. To do. Thereby, not only the improvement of the grain boundary strength by Mo or Nb but also the reduction of the embrittlement strength of the grain boundaries can be suppressed.

　さらに、コイル巻取条件を制御することで、固溶Ｍｏ及びＮｂの効果により、オーステナイトの強度を上昇させることができる。加えて、オーステナイトから下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトへと相変態する際に、変態により発生する応力を緩和する有利な結晶方位が優先的に生成する。これにより、ホットスタンプ用鋼鈑において、下部ベイナイト、マルテンサイト及び焼戻しマルテンサイトの結晶粒の｛１１２｝＜１１１＞のＸ線ランダム強度比を制御することができる。 Furthermore, by controlling the coil winding conditions, the strength of austenite can be increased due to the effects of solute Mo and Nb. In addition, when crystallizing from austenite to lower bainite, martensite, and tempered martensite, advantageous crystal orientations that relieve stress generated by the transformation are preferentially generated. Thereby, the {112} <111> X-ray random intensity ratio of the crystal grains of the lower bainite, martensite and tempered martensite can be controlled in the hot stamping steel sheet.

　このような特徴を持つホットスタンプ用鋼鈑をホットスタンプ工程に供することにより、オーステナイトとマルテンサイトのテクスチャーメモリー効果によって、ホットスタンプ成形体において、下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を８０％以上生成させる。 By subjecting the hot stamping steel plate having such characteristics to the hot stamping process, the texture memory effect of austenite and martensite causes the lower bainite, martensite, and tempered martensite crystal grains to be formed. Of the grain boundaries having a rotation angle of 5 ° to 75 ° with the <011> direction as the rotation axis, 80% or more of the grain boundaries having a rotation angle of 15 ° or more are generated.

　本発明では、ホットスタンプ工程において、下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトの結晶粒界をオーステナイトの逆変態サイトとして活用することにより、ホットスタンプ用鋼鈑で発現させた結晶方位制御をホットスタンプ成形体へと引き継ぐことができる。 In the present invention, in the hot stamping process, the crystal orientation control expressed in the steel sheet for hot stamping is hot stamped by utilizing the grain boundaries of lower bainite, martensite, and tempered martensite as austenite reverse transformation sites. It can be handed over to the molded body.

　以下、本発明のホットスタンプ成形体とその製造方法について説明する。 Hereinafter, the hot stamping molded body of the present invention and the manufacturing method thereof will be described.

　まず、本発明のホットスタンプ成形体を構成する成分組成の限定理由について説明する。以下、成分組成に係る％は質量％を意味する。 First, the reason for limiting the component composition constituting the hot stamping molded body of the present invention will be described. Hereinafter,% related to the component composition means mass%.

　「Ｃ：０．３５％以上、０．７５％以下」
　Ｃは、２０００ＭＰａ以上の引張強さを得るために重要な元素である。０．３５％未満では、マルテンサイトが軟らかく、２０００ＭＰａ以上の引張強さを確保することが困難であるので、Ｃは０．３５％以上とする。好ましくは０．３７％以上である。上限は特に定めないが、要求される強度と早期破断抑制のバランスを鑑みて、上限を０．７５％とする。 "C: 0.35% or more, 0.75% or less"
C is an important element for obtaining a tensile strength of 2000 MPa or more. If it is less than 0.35%, martensite is soft and it is difficult to ensure a tensile strength of 2000 MPa or more, so C is 0.35% or more. Preferably it is 0.37% or more. Although the upper limit is not particularly defined, the upper limit is set to 0.75% in view of the balance between required strength and early fracture suppression.

　「Ｓｉ：０．００５％以上、０．２５％以下」
　Ｓｉは、曲げ変形能を高めて衝撃吸収能の向上に寄与する元素である。０．００５％未満では曲げ変形能が乏しく衝撃吸収能が劣化するため、０．００５％以上添加する。好ましくは０．０１％以上である。一方、０．２５％を超えると、炭化物への固溶量が増加して炭化物が溶解しにくくなり、溶け残った炭化物がオーステナイトの逆変態サイトとなってしまい、下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を８０％以上に制御できなくなるため、上限を０．２５％とする。好ましくは０．２２％以下である。 “Si: 0.005% or more, 0.25% or less”
Si is an element that enhances the bending deformability and contributes to the improvement of the shock absorbing ability. If it is less than 0.005%, the bending deformability is poor and the impact absorbing ability deteriorates, so 0.005% or more is added. Preferably it is 0.01% or more. On the other hand, if it exceeds 0.25%, the amount of solid solution in the carbide increases and the carbide becomes difficult to dissolve, and the undissolved carbide becomes a reverse transformation site of austenite, and lower bainite, martensite or tempered martensite. Of the grain boundaries whose rotation angle is 5 ° or more and 75 ° or less with the <011> direction of the crystal grains of the site as the rotation axis, the grain boundary where the rotation angle is 15 ° or more cannot be controlled to 80% or more. Is 0.25%. Preferably it is 0.22% or less.

　「Ｍｎ：０．５％以上、３．０％以下」
　Ｍｎは、固溶強化で強度の向上に寄与する元素である。０．５％未満では固溶強化能が乏しくマルテンサイトが軟らかくなり、２０００ＭＰａ以上の引張強さを確保することが困難であるので、０．５％以上添加する。好ましくは０．７％以上である。一方、３．０％を超えて添加すると、炭化物への固溶量が増加して炭化物が溶解しにくくなり、溶け残った炭化物がオーステナイトの逆変態サイトとなってしまい、下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を８０％以上に制御できなくなるため、３．０％を上限とする。好ましくは、２．５％以下である。 “Mn: 0.5% to 3.0%”
Mn is an element that contributes to improvement in strength by solid solution strengthening. If it is less than 0.5%, the solid solution strengthening ability is poor and the martensite becomes soft, and it is difficult to ensure a tensile strength of 2000 MPa or more, so 0.5% or more is added. Preferably it is 0.7% or more. On the other hand, if added over 3.0%, the amount of solid solution in the carbide increases and the carbide becomes difficult to dissolve, and the undissolved carbide becomes a reverse transformation site of austenite, and lower bainite or martensite or Among the grain boundaries having a rotation angle of 5 ° or more and 75 ° or less with the <011> direction of the tempered martensite crystal grains as the rotation axis, the grain boundary having a rotation angle of 15 ° or more cannot be controlled to 80% or more. 3.0% is the upper limit. Preferably, it is 2.5% or less.

　「ｓｏｌ．Ａｌ：０．０００２％以上、３．０％以下」
　Ａｌは、溶鋼を脱酸して鋼を健全化する作用をなす元素である。０．０００２％未満では、脱酸が十分で粗大な酸化物が生成して早期破断を引き起こすため、ｓｏｌ．Ａｌは０．０００２％以上とする。好ましくは０．００１０％以上である。一方、３．０％を超えて添加すると、粗大な酸化物が生成し早期破断を引き起こすため、３．０％以下とする。好ましくは２．５％以下、より好ましくは０．５％以下である。 “Sol.Al: 0.0002% or more, 3.0% or less”
Al is an element that acts to deoxidize molten steel and to make the steel sound. If it is less than 0.0002%, deoxidation is sufficient and a coarse oxide is generated, causing premature breakage. Al is made 0.0002% or more. Preferably it is 0.0010% or more. On the other hand, if added over 3.0%, a coarse oxide is generated and causes early breakage, so the content is made 3.0% or less. Preferably it is 2.5% or less, More preferably, it is 0.5% or less.

　「Ｃｒ：０．０５％以上、１．００％以下」
　Ｃｒは、固溶強化で強度の向上に寄与する元素である。０．０５％未満では固溶強化能が乏しくマルテンサイトが軟らかくなり、２０００ＭＰａ以上の引張強さを確保することが困難であるので、０．０５％以上添加する。好ましくは０．１％以上である。一方、１．００％を超えて添加すると、炭化物への固溶量が増加して炭化物が溶解しにくくなり、溶け残った炭化物がオーステナイトの逆変態サイトとなってしまい、下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を８０％以上に制御できなくなるため、１．００％を上限とする。好ましくは、０．８％以下である。 "Cr: 0.05% or more, 1.00% or less"
Cr is an element that contributes to improvement in strength by solid solution strengthening. If it is less than 0.05%, the solid solution strengthening ability is poor, the martensite becomes soft, and it is difficult to ensure a tensile strength of 2000 MPa or more, so 0.05% or more is added. Preferably it is 0.1% or more. On the other hand, if added over 1.00%, the amount of solid solution in the carbide increases and the carbide becomes difficult to dissolve, and the undissolved carbide becomes a reverse transformation site of austenite, and lower bainite or martensite or Among the grain boundaries having a rotation angle of 5 ° or more and 75 ° or less with the <011> direction of the tempered martensite crystal grains as the rotation axis, the grain boundary having a rotation angle of 15 ° or more cannot be controlled to 80% or more. The upper limit is 1.00%. Preferably, it is 0.8% or less.

　「Ｂ：０．０００５％以上、０．０１０％以下」
　Ｂは、固溶強化で強度の向上に寄与する元素である。０．０００５％未満では固溶強化能が乏しくマルテンサイトが軟らかくなり、２０００ＭＰａ以上の引張強さを確保することが困難であるので、０．０００５％以上添加する。好ましくは０．０００８％以上である。一方、０．０１０％を超えて添加すると、炭化物への固溶量が増加して炭化物が溶解しにくくなり、溶け残った炭化物がオーステナイトの逆変態サイトとなってしまい、下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を８０％以上に制御できなくなるため、０．０１０％を上限とする。好ましくは、０．００７％以下である。 “B: 0.0005% or more and 0.010% or less”
B is an element that contributes to improving the strength by solid solution strengthening. If it is less than 0.0005%, the solid solution strengthening ability is poor and the martensite becomes soft, and it is difficult to ensure a tensile strength of 2000 MPa or more, so 0.0005% or more is added. Preferably it is 0.0008% or more. On the other hand, if added over 0.010%, the amount of solid solution in the carbide increases and the carbide becomes difficult to dissolve, and the undissolved carbide becomes a reverse transformation site of austenite, and lower bainite or martensite or Among the grain boundaries having a rotation angle of 5 ° or more and 75 ° or less with the <011> direction of the tempered martensite crystal grains as the rotation axis, the grain boundary having a rotation angle of 15 ° or more cannot be controlled to 80% or more. 0.010% is the upper limit. Preferably, it is 0.007% or less.

　「Ｎｂ：０．０１％以上、０．１５％以下」
　Ｎｂは、旧オーステナイトの粒界に固溶して粒界の強度を上昇させる元素である。また、Ｎｂは、粒界に固溶することでＰの粒界偏析を阻害するため、粒界の脆化強度を向上させる。そのため、０．０１％以上添加する。好ましくは０．０３０％以上である。一方、０．１５％を超えて添加すると、炭化物として析出しやすくなり、ホットスタンプ用鋼鈑において、下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の｛１１２｝＜１１１＞のＸ線ランダム強度比を２．８以上とすることができず、結果として、下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を８０％以上に制御できなくなるため、０．１５％以下とする。好ましくは０．１２％以下である。 “Nb: 0.01% or more and 0.15% or less”
Nb is an element that dissolves in the grain boundary of prior austenite and increases the strength of the grain boundary. In addition, Nb improves the embrittlement strength of the grain boundary because it dissolves at the grain boundary and inhibits P grain boundary segregation. Therefore, 0.01% or more is added. Preferably it is 0.030% or more. On the other hand, if added over 0.15%, it becomes easy to precipitate as carbide, and in the hot stamping steel plate, the {112} <111> X-ray random strength of the crystal grains of lower bainite, martensite or tempered martensite The grain boundary where the ratio cannot be 2.8 or more, and as a result, the rotation angle is 5 ° or more and 75 ° or less with the <011> direction of the crystal grains of lower bainite, martensite, or tempered martensite as the rotation axis. Of these, the grain boundary where the rotation angle is 15 ° or more cannot be controlled to 80% or more, so it is 0.15% or less. Preferably it is 0.12% or less.

　「Ｍｏ：０．００５％以上、１．００％以下」
　Ｍｏは、旧オーステナイトの粒界に固溶して粒界の強度を上昇させる元素である。また、Ｍｏは、粒界に固溶することでＰの粒界偏析を阻害するため、粒界の脆化強度を向上させる。そのため、０．００５以上添加する。好ましくは０．０３０％以上である。一方、１．００％を超えて添加すると、炭化物として析出しやすくなり、炭化物として析出しやすくなり、ホットスタンプ用鋼鈑において、下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の｛１１２｝＜１１１＞のＸ線ランダム強度比を２．８以上とすることができず、結果として、下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を８０％以上に制御できなくなるため、１．００％以下とする。好ましくは０．８０％以下である。 “Mo: 0.005% or more and 1.00% or less”
Mo is an element that dissolves in the grain boundary of prior austenite and increases the strength of the grain boundary. Moreover, since Mo inhibits P grain boundary segregation by forming a solid solution at the grain boundary, the embrittlement strength of the grain boundary is improved. Therefore, 0.005 or more is added. Preferably it is 0.030% or more. On the other hand, when added over 1.00%, it becomes easy to precipitate as carbide, and it becomes easy to precipitate as carbide. In the steel sheet for hot stamping, {112} <of the grains of lower bainite, martensite or tempered martensite The X-ray random intensity ratio of 111> cannot be made 2.8 or more. As a result, the rotation angle is 5 ° or more with the <011> direction of the crystal grains of lower bainite, martensite, or tempered martensite as the rotation axis. Of the grain boundaries that are 75 ° or less, the grain boundaries that have a rotation angle of 15 ° or more cannot be controlled to 80% or more. Preferably it is 0.80% or less.

　「Ｔｉ：０％以上、０．１５％以下」
　Ｔｉは、必須の元素ではないが、固溶強化で強度の向上に寄与する元素であるため、必要に応じて添加してもよい。Ｔｉを添加する場合、添加の効果を得るためには、０．０１％以上とするのが好ましい。好ましくは０．０２％以上である。一方、０．１５％を超えて添加すると、粗大な炭化物や窒化物を形成して早期破断を引き起こすため、０．１５％以下とする。好ましくは０．１２％以下である。 "Ti: 0% or more, 0.15% or less"
Ti is not an essential element, but Ti is an element that contributes to improvement in strength by solid solution strengthening, and may be added as necessary. When adding Ti, in order to acquire the effect of addition, it is preferable to set it as 0.01% or more. Preferably it is 0.02% or more. On the other hand, if added over 0.15%, coarse carbides and nitrides are formed to cause early breakage, so the content is made 0.15% or less. Preferably it is 0.12% or less.

　「Ｎｉ：０％以上、３．００％以下」
　Ｎｉは、必須の元素ではないが、固溶強化で強度の向上に寄与する元素であるため、必要に応じて添加してもよい。Ｎｉを添加する場合、添加の効果を得るためには、０．０１％以上とするのが好ましい。好ましくは０．０２％以上である。一方、３．００％を超えて添加すると、鋼が脆くなり早期破断を引き起こすため、３．００％以下とする。好ましくは２．００％以下である。 "Ni: 0% or more and 3.00% or less"
Although Ni is not an essential element, it is an element that contributes to improvement in strength by solid solution strengthening, and may be added as necessary. When adding Ni, in order to acquire the effect of addition, it is preferable to set it as 0.01% or more. Preferably it is 0.02% or more. On the other hand, if added over 3.00%, the steel becomes brittle and causes premature fracture, so the content is made 3.00% or less. Preferably it is 2.00% or less.

　「Ｐ：０．１０％以下」
　Ｐは不純物元素であり、粒界に偏析しやすく、粒界の脆化強度を低下させる元素である。０．１０％を超えると、粒界の脆化強度が著しく低下し、早期破断を引き起こすため、Ｐは０．１０％以下とする。好ましくは０．０５０％以下である。下限は、特に限定しないが、０．０００１％未満に低減すると、脱Ｐコストが大幅に上昇し、経済的に不利になるので、実用鋼板上、０．０００１％が実質的な下限である。 “P: 0.10% or less”
P is an impurity element and is an element that easily segregates at the grain boundary and lowers the embrittlement strength of the grain boundary. If it exceeds 0.10%, the embrittlement strength of the grain boundary is remarkably lowered and premature fracture is caused, so P is made 0.10% or less. Preferably it is 0.050% or less. The lower limit is not particularly limited, but if it is reduced to less than 0.0001%, the de-P cost increases significantly and becomes economically disadvantageous, so 0.0001% is a practical lower limit on a practical steel sheet.

　「Ｓ：０．１０％以下」
　Ｓは不純物元素であり、介在物を形成する元素である。０．１０％を超えると、介在物が生成し早期破断を引き起こすため、Ｓは０．１０％以下とする。好ましくは０．００５０％以下である。下限は、特に限定しないが、０．００１５％未満に低減すると、脱Ｓコストが大幅に上昇し、経済的に不利になるので、実用鋼板上、０．００１５％が実質的な下限である。 “S: 0.10% or less”
S is an impurity element and is an element that forms inclusions. If it exceeds 0.10%, inclusions are generated and cause early breakage, so S is made 0.10% or less. Preferably it is 0.0050% or less. The lower limit is not particularly limited, but if it is reduced to less than 0.0015%, the de-S cost is significantly increased, which is economically disadvantageous, so 0.0015% is a practical lower limit on a practical steel sheet.

　「Ｎ：０．０１０％以下」
　Ｎは不純物元素であり、窒化物を形成して早期破断を引き起こすため、０．０１０％以下とする。好ましくは０．００７５％以下である。下限は、特に限定しないが、０．０００１％未満に低減すると、脱Ｎコストが大幅に上昇し、経済的に不利になるので、実用鋼板上、０．０００１％が実質的な下限である。 “N: 0.010% or less”
N is an impurity element, and forms nitrides and causes early breakage. Therefore, the N content is set to 0.010% or less. Preferably it is 0.0075% or less. The lower limit is not particularly limited, but if it is reduced to less than 0.0001%, the de-N cost greatly increases and becomes economically disadvantageous, so 0.0001% is a practical lower limit on a practical steel sheet.

　成分組成の残部は、Ｆｅ及び不純物である。不純物としては、鋼原料もしくはスクラップから及び／又は製鋼過程で不可避的に混入し、本発明のホットスタンプ成形体の特性を阻害しない範囲で許容される元素が例示される。 The balance of the component composition is Fe and impurities. Examples of impurities include elements that are allowed from steel raw materials or scraps and / or inevitably mixed in the steel making process, and are allowed to the extent that they do not impair the properties of the hot stamped article of the present invention.

　次に、本発明のホットスタンプ成形体のミクロ組織の限定理由について説明する。 Next, the reason for limiting the microstructure of the hot stamping molded body of the present invention will be described.

　「下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として、回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を８０％以上」 “A grain boundary having a rotation angle of 15 ° or more among grain boundaries having a rotation angle of 5 ° to 75 ° with the <011> direction of the crystal grains of lower bainite, martensite, and tempered martensite as the rotation axis. Over 80% "

　下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトの結晶粒の方位制御は、優れた曲げ変形能を確保するために重要な組織因子である。本発明者らの検討によれば、ホットスタンプ成形体に要求される衝撃吸収能を得るためには、下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として、回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を増加させる程好ましく、割合として８０％以上に制御する必要がある。より好ましくは８５％以上である。 Control of crystal orientation of lower bainite, martensite, and tempered martensite is an important structural factor for ensuring excellent bending deformability. According to the study by the present inventors, in order to obtain the impact absorbing ability required for the hot stamped molded body, the <011> direction of the crystal grains of the lower bainite, martensite, and tempered martensite is used as the rotation axis. Of the grain boundaries having a rotation angle of 5 ° or more and 75 ° or less, it is preferable to increase the grain boundaries having a rotation angle of 15 ° or more, and the ratio needs to be controlled to 80% or more. More preferably, it is 85% or more.

　下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界の割合は、次のように測定する。 Of the grain boundaries whose rotation angle is 5 ° or more and 75 ° or less with the <011> direction of the crystal grains of lower bainite, martensite, or tempered martensite as the rotation axis, the ratio of the grain boundary where the rotation angle is 15 ° or more is Measure as follows.

　ホットスタンプ成形体の中央部から、その板面に垂直な断面（板厚断面）が観察できるようにサンプルを切り出す。＃６００から＃１５００の炭化珪素ペーパーを使用して測定面を研磨した後、粒度１μｍから６μｍのダイヤモンドパウダーをアルコール等の希釈液や純水に分散させた液体を使用して鏡面に仕上げる。 ¡Cut out a sample from the center of the hot stamping body so that a cross section perpendicular to the plate surface (plate thickness cross section) can be observed. After polishing the measurement surface using # 600 to # 1500 silicon carbide paper, a mirror surface is finished using a liquid in which a diamond powder having a particle size of 1 μm to 6 μm is dispersed in a diluent such as alcohol or pure water.

　次に、標準コロイドシリカ懸濁液（粒径０．０４μｍ）を使用して、８～２０分の仕上げ研磨を行う。 Next, finish polishing is performed for 8 to 20 minutes using a standard colloidal silica suspension (particle size: 0.04 μm).

　研磨後の試料をアセトンまたはエチルアルコールで洗浄した後に乾燥させ、走査型電子顕微鏡内にセットする。使用する走査型電子顕微鏡は、ＥＢＳＤ検出器（ＴＳＬ製ＤＶＣ５型検出器）を装備した機種を用いる。 洗浄 The polished sample is washed with acetone or ethyl alcohol, dried, and set in a scanning electron microscope. The scanning electron microscope used is a model equipped with an EBSD detector (TSL DVC5 detector).

　サンプルの板厚３／８位置～５／８位置において、板厚方向に５０μｍ、圧延方向に５０μｍの範囲を、０．１μｍの測定間隔でＥＢＳＤ測定して結晶方位情報を得る。測定条件は、真空レベルが９．６×１０－5以下、加速電圧が１５ｋＶ、照射電流が１３ｎＡ、Ｂｉｎｎｉｎｇ サイズが４×４、露光時間を４２秒とする。 Crystal orientation information is obtained by EBSD measurement at a measurement interval of 0.1 μm in a range of 50 μm in the plate thickness direction and 50 μm in the rolling direction at the plate thickness 3/8 position to 5/8 position. The measurement conditions are a vacuum level of 9.6 × 10 −5 or less, an acceleration voltage of 15 kV, an irradiation current of 13 nA, a Binning size of 4 × 4, and an exposure time of 42 seconds.

　測定データをＥＢＳＤ解析装置に付属のソフトウェア「ＯＩＭ　Ａｎａｌｙｓｉｓ（登録商標）」に搭載された「Ｉｎｖｅｒｓｅ　Ｐｏｌｅ　Ｆｉｇｕｒｅ　Ｍａｐ」および「Ａｘｉｓ　Ａｎｇｌｅ」機能を用い、体心立方構造を持つ結晶粒の粒界のうち、＜０１１＞方向を回転軸として回転角が５°以上７５°以下である粒界の長さを算出する。 Using the “Inverse Pole Figure Map” and “Axis Angle” functions included in the software “OIM Analysis (registered trademark)” attached to the EBSD analyzer, the measurement data is among the grain boundaries of the body-centered cubic structure. The length of the grain boundary whose rotation angle is 5 ° or more and 75 ° or less with the <011> direction as the rotation axis is calculated.

　次に、＜０１１＞方向を回転軸として回転角が１５°以上７５°以下である粒界の長さを算出し、＜０１１＞方向を回転軸として回転角が５°以上７５°以下である粒界の長さで除した値を算出する。 Next, the length of the grain boundary having a rotation angle of 15 ° to 75 ° with the <011> direction as the rotation axis is calculated, and the rotation angle is 5 ° to 75 ° with the <011> direction as the rotation axis. The value divided by the grain boundary length is calculated.

　上記測定を少なくとも５か所以上実施し、その平均値を、下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界の割合とする。 Grain boundaries where the above measurement is carried out at least 5 locations, and the average value is a grain boundary where the rotation angle is 5 ° or more and 75 ° or less with the <011> direction of the crystal grains of lower bainite, martensite or tempered martensite as the rotation axis Of these, the ratio of grain boundaries where the rotation angle is 15 ° or more is used.

　「ミクロ組織の面積率で９０％以上が、下部ベイナイト、マルテンサイト及び焼戻しマルテンサイトの１種以上である」 "90% or more of the area ratio of the microstructure is one or more of lower bainite, martensite and tempered martensite"

　ホットスタンプ成形体が１５００ＭＰａ以上の引張強度を得るためには、ミクロ組織が面積率で９０％以上のマルテンサイト又は焼戻しマルテンサイトを含む必要がある。好ましくは９４％以上である。引張強度を確保する観点では、ミクロ組織は下部ベイナイトでもよい。面積率９０％以上の組織は、下部ベイナイト、マルテンサイト及び焼戻しマルテンサイトのうちの１種でもよいし、これらの混合組織でもよい。 In order for the hot stamping molded body to obtain a tensile strength of 1500 MPa or more, the microstructure needs to contain martensite or tempered martensite having an area ratio of 90% or more. Preferably it is 94% or more. From the viewpoint of securing tensile strength, the microstructure may be lower bainite. The structure having an area ratio of 90% or more may be one of lower bainite, martensite, and tempered martensite, or a mixed structure thereof.

　ミクロ組織の残部は特に規定せず、例えば、上部ベイナイト、残留オーステナイト、パーライトが挙げられる。 The balance of the microstructure is not particularly specified, and examples thereof include upper bainite, retained austenite, and pearlite.

　下部ベイナイト、マルテンサイト、焼戻しマルテンサイトの面積率は、次のように測定する。 The area ratio of lower bainite, martensite, and tempered martensite is measured as follows.

　ホットスタンプ成形体の中央から板面に垂直な断面を切り出し、＃６００から＃１５００の炭化珪素ペーパーを使用して測定面を研磨した後、粒度１～６μｍのダイヤモンドパウダーをアルコール等の希釈液や純水に分散させた液体を使用して鏡面に仕上げる。 A section perpendicular to the plate surface is cut out from the center of the hot stamped body, and the measurement surface is polished using # 600 to # 1500 silicon carbide paper, and then a diamond powder having a particle size of 1 to 6 μm is diluted with a diluent such as alcohol or the like. Use a liquid dispersed in pure water to give a mirror finish.

　１．５～３％硝酸－アルコール溶液に５～１０秒間浸漬し、高傾角粒界を現出させる。この際、腐食作業は排気処理装置内で実施し、作業雰囲気の温度は常温とする。 Immerse in a 1.5-3% nitric acid-alcohol solution for 5-10 seconds to reveal high-angle grain boundaries. At this time, the corrosive work is performed in the exhaust treatment apparatus, and the temperature of the working atmosphere is a normal temperature.

　腐食後の試料をアセトンまたはエチルアルコールで洗浄した後に乾燥させ、走査型電子顕微鏡観察に供する。使用する走査型電子顕微鏡は、２電子検出器を装備しているものとする。９．６×１０－５以下の真空において、加速電圧１０ｋＶ、照射電流レベル８にて試料に電子線を照射し、試料の板厚１／４位置を中心として１／８～３／８位置の範囲の２次電子像を撮影する。撮影倍率は横３８６ｍｍ×縦２９０ｍｍの画面を基準として１００００倍撮影視野数は１０視野以上とする。 The corroded sample is washed with acetone or ethyl alcohol, dried, and subjected to observation with a scanning electron microscope. The scanning electron microscope used is assumed to be equipped with a two-electron detector. In a vacuum of 9.6 × 10 −5 or less, the sample was irradiated with an electron beam at an acceleration voltage of 10 kV and an irradiation current level of 8, and the sample thickness was 1/8 to 3/8 centered on the 1/4 position. A secondary electron image of the range is taken. The photographing magnification is 10,000 times on the basis of a screen of 386 mm wide × 290 mm long, and the number of photographing fields is 10 fields or more.

　撮影した２次電子像においては、結晶粒界と炭化物が明るいコントラストとして撮像されるため、結晶粒界と炭化物の位置により、簡便に組織を判定することができる。結晶粒の内部に炭化物が形成している場合は、焼戻しマルテンサイト又は下部ベイナイトであり、結晶粒に内部に炭化物が観察されない組織はマルテンサイトである。 In the photographed secondary electron image, the crystal grain boundary and the carbide are captured with a bright contrast, and therefore the structure can be easily determined by the position of the crystal grain boundary and the carbide. When carbide is formed inside the crystal grain, it is tempered martensite or lower bainite, and the structure where the carbide is not observed inside the crystal grain is martensite.

　一方、結晶粒界に炭化物が形成している組織は上部ベイナイトまたはパーライトである。 On the other hand, the structure in which carbides are formed at the grain boundaries is upper bainite or pearlite.

　残留オーステナイトについては、上記ミクロ組織とは結晶構造が異なるため、２次電子像を撮像した位置と同一の視野を電子後方散乱回折法にて測定する。使用する走査型電子顕微鏡は、電子後方散乱回折法が可能なカメラを装備しているものとする。９．６×１０－５以下の真空において、加速電圧２５ｋＶ、照射電流レベル１６にて試料に電子線を照射して測定を行い、得られた測定データから面心立方格子のマップを作成する。 Since the retained austenite has a crystal structure different from that of the above microstructure, the same field of view as the position where the secondary electron image is taken is measured by an electron backscatter diffraction method. The scanning electron microscope to be used is equipped with a camera capable of electron backscatter diffraction. In a vacuum of 9.6 × 10 −5 or less, the sample is irradiated with an electron beam at an acceleration voltage of 25 kV and an irradiation current level of 16, and a face-centered cubic lattice map is created from the obtained measurement data.

　撮影倍率は横３８６ｍｍ×縦２９０ｍｍの画面を基準として１００００倍で撮像した写真上に２μｍ間隔のメッシュを作成し、メッシュの交点に位置するミクロ組織を選別していく。各組織の交点数を全ての交点で除した値を当該ミクロ組織の面積分率とする。この操作を１０視野で行い、平均値を算出し、ミクロ組織の面積率とする。 * The imaging magnification is to create a mesh of 2 μm intervals on a photograph taken at a magnification of 10,000 with reference to a screen of horizontal 386 mm × longitudinal 290 mm, and select a microstructure located at the intersection of the mesh. A value obtained by dividing the number of intersections of each structure by all the intersections is defined as the area fraction of the microstructure. This operation is performed in 10 fields of view, and the average value is calculated as the area ratio of the microstructure.

　「ホットスタンプ用鋼鈑の製造方法」
　次に、本発明に係るホットスタンプ成形体、およびホットスタンプ成形体の製造に用いるホットスタンプ用鋼板を得るための製造方法の形態を説明するが、本発明は、以下に説明するような形態に限定されない。 "Method for manufacturing hot stamping steel"
Next, although the form of the manufacturing method for obtaining the hot stamping molded object which concerns on this invention, and the hot stamping steel plate used for manufacture of a hot stamping molded object is demonstrated, this invention is in the form which is demonstrated below. It is not limited.

　＜ホットスタンプ用鋼板の製造方法＞ <Method for manufacturing steel sheet for hot stamping>

　（１）連続鋳造工程
　上述の化学組成を有する溶鋼を連続鋳造法により、鋼片（スラブ）にする。この連続鋳造工程では、単位時間当たりの溶鋼鋳込み量を６ｔｏｎ／分以下とすることが好ましい。連続鋳造時に溶鋼の単位時間あたりの鋳込み量（鋳込み速度）が６ｔｏｎ／分を超えると、Ｍｎのミクロ偏析が増加するとともに、ＭｏやＮｂを主体とする析出物の核生成量が増加してしまう。鋳込み量を５ｔｏｎ／分を以下とすることがさらに好ましい。鋳込み量の下限は特に限定されないが、操業コストの観点から、０．１ｔｏｎ／分以上であることが好ましい。 (1) Continuous casting process The molten steel which has the above-mentioned chemical composition is made into a steel piece (slab) by a continuous casting method. In this continuous casting process, it is preferable to set the molten steel casting amount per unit time to 6 ton / min or less. When the casting amount (casting speed) per unit time of molten steel exceeds 6 ton / min during continuous casting, microsegregation of Mn increases and the nucleation amount of precipitates mainly composed of Mo and Nb increases. . More preferably, the casting amount is 5 ton / min or less. The lower limit of the casting amount is not particularly limited, but is preferably 0.1 ton / min or more from the viewpoint of operation cost.

　（２）熱間圧延工程
　上述の鋼片を熱間圧延して鋼板とする。その際、式（２）で定義されるＡ３変態温度＋１０℃以上かつＡ３変態温度＋２００℃以下の温度域で熱間圧延を終了し、その際の最終段圧下率を１２％以上とし、仕上げ圧延終了後から１秒以内に冷却を開始し、仕上げ圧延終了温度から５５０℃までの温度域を１００℃／秒以上の冷却速度で冷却し、５００℃未満の温度で巻き取る。 (2) Hot rolling process The above-mentioned steel slab is hot-rolled to obtain a steel plate. At that time, the hot rolling is finished in a temperature range defined by the formula (2) of A3 transformation temperature + 10 ° C. or more and A3 transformation temperature + 200 ° C. or less, and the final rolling reduction at that time is set to 12% or more. Cooling is started within 1 second after the completion, and the temperature range from the finish rolling finish temperature to 550 ° C. is cooled at a cooling rate of 100 ° C./second or more and wound at a temperature of less than 500 ° C.

　Ａ３変態温度＝８５０＋１０×（Ｃ＋Ｎ）×Ｍｎ＋３５０×Ｎｂ＋２５０×Ｔｉ＋４０×Ｂ＋１０×Ｃｒ＋１００×Ｍｏ　・・・・式（２） A3 transformation temperature = 850 + 10 × (C + N) × Mn + 350 × Nb + 250 × Ti + 40 × B + 10 × Cr + 100 × Mo (2)

　仕上げ圧延温度をＡ３変態温度＋１０℃以上とすることにより、オーステナイトの再結晶を促進させる。これにより、結晶粒内における小傾角粒界の形成が抑制され、Ｎｂ、Ｍｏの析出サイトを減少させることができる。また、Ｎｂ、Ｍｏの析出サイトを減少させることにより、Ｃの消費も抑制できるため、後の工程において、炭化物の個数密度を高めることができる。好ましくは、Ａ３変態温度＋３０℃以上である。 The recrystallization of austenite is promoted by setting the finish rolling temperature to A3 transformation temperature + 10 ° C. or higher. Thereby, the formation of a low-angle grain boundary in the crystal grains is suppressed, and the precipitation sites of Nb and Mo can be reduced. In addition, since the consumption of C can be suppressed by reducing the precipitation sites of Nb and Mo, the number density of carbides can be increased in a later step. Preferably, it is A3 transformation temperature + 30 ° C. or higher.

　仕上げ圧延温度をＡ３変態温度＋２００℃以下とすることにより、オーステナイトの過度な粒成長を抑制する。Ａ３変態温度＋２００℃以下の温度域で仕上げ圧延することにより、オーステナイトの再結晶が促進され、なおなつ、過度な粒成長も起こらないため、巻き取り工程において、微細な炭化物を得ることができる。好ましくは、Ａ３変態温度＋１５０℃以下である。 By setting the finish rolling temperature to A3 transformation temperature + 200 ° C. or less, excessive grain growth of austenite is suppressed. By performing finish rolling in a temperature range of A3 transformation temperature + 200 ° C. or less, recrystallization of austenite is promoted, and excessive grain growth does not occur. Therefore, fine carbides can be obtained in the winding process. Preferably, it is A3 transformation temperature +150 degrees C or less.

　仕上げ圧延の圧下率を１２％以上とすることにより、オーステナイトの再結晶を促進させる。これにより、結晶粒内における小傾角粒界の形成が抑制され、Ｎｂ、Ｍｏの析出サイトを減少させることができる。好ましくは、１５％以上である。 Austenite recrystallization is promoted by setting the reduction ratio of finish rolling to 12% or more. Thereby, the formation of a low-angle grain boundary in the crystal grains is suppressed, and the precipitation sites of Nb and Mo can be reduced. Preferably, it is 15% or more.

　仕上げ圧延終了後から１秒以内、好ましくは０．８秒以内に冷却を開始し、仕上げ圧延終了温度から５５０℃までの温度域を１００℃／秒以上の冷却速度で冷却することにより、ＮｂおよびＭｎの析出が促進される温度域での停留時間を減少させることができる。その結果、オーステナイト中でのＮｂ、Ｍｏの析出を抑制させることができ、オーステナイト粒界におけるＮｂおよびＭｏの固溶量が増加する。 By starting cooling within 1 second after finishing rolling, preferably within 0.8 seconds, and cooling the temperature range from the finishing rolling finishing temperature to 550 ° C. at a cooling rate of 100 ° C./second or more, Nb and The residence time in the temperature range where the precipitation of Mn is promoted can be reduced. As a result, precipitation of Nb and Mo in austenite can be suppressed, and the amount of Nb and Mo dissolved in the austenite grain boundary increases.

　巻き取り温度を５００℃未満とすることにより、上記効果を高めるとともに、ホットスタンプ用鋼鈑において、結晶粒の｛１１２｝＜１１１＞のＸ線ランダム強度比を制御することができる。また、仕上げ圧延直後では、ＮｂやＭｏはオーステナイト中に固溶しており、ＮｂやＭｏを固溶したオーステナイトから、下部ベイナイト、マルテンサイト、又は焼戻しマルテンサイトへと変態させることにより、Ｎｂ、Ｍｏが変態により発生する応力を緩和するために有利な結晶方位を優先的に生成させるので、結晶粒の｛１１２｝＜１１１＞のＸ線ランダム強度比を制御することができる。好ましくは４８０℃未満である。下限は特に定めないが、室温以下で巻き取ることは実操業上困難であるため、室温が下限となる。 By setting the coiling temperature to less than 500 ° C., the above effect can be enhanced, and the {112} <111> X-ray random intensity ratio of the crystal grains can be controlled in the hot stamping steel sheet. Further, immediately after finish rolling, Nb and Mo are dissolved in austenite. By transforming from austenite in which Nb and Mo are dissolved to lower bainite, martensite, or tempered martensite, Nb, Mo Produces a crystal orientation that is advantageous in order to relieve the stress generated by transformation, so that the {112} <111> X-ray random intensity ratio of the crystal grains can be controlled. Preferably it is less than 480 degreeC. The lower limit is not particularly defined, but it is difficult to wind up at room temperature or lower in actual operation, so the room temperature is the lower limit.

　（３）めっき層の形成
　軟化層の表面上に、耐食性の向上等を目的として、めっき層を形成してもよい。めっき層は、電気めっき層及び溶融めっき層のいずれでもよい。電気めっき層としては、電気亜鉛めっき層、電気Ｚｎ－Ｎｉ合金めっき層等が例示される。溶融めっき層としては、溶融亜鉛めっき層、合金化溶融亜鉛めっき層、溶融アルミニウムめっき層、溶融Ｚｎ－Ａｌ合金めっき層、溶融Ｚｎ－Ａｌ－Ｍｇ合金めっき層、溶融Ｚｎ－Ａｌ－Ｍｇ－Ｓｉ合金めっき層等が例示される。めっき層の付着量は、特に制限されず一般的な付着量でよい。 (3) Formation of plating layer A plating layer may be formed on the surface of the softening layer for the purpose of improving corrosion resistance. The plating layer may be either an electroplating layer or a hot dipping layer. Examples of the electroplating layer include an electrogalvanizing layer and an electro Zn—Ni alloy plating layer. The hot dip galvanized layer includes hot dip galvanized layer, alloyed hot dip galvanized layer, hot dip aluminum plated layer, hot dip Zn-Al alloy plated layer, hot dip Zn-Al-Mg alloy plated layer, hot dip Zn-Al-Mg-Si alloy. A plating layer etc. are illustrated. The adhesion amount of the plating layer is not particularly limited and may be a general adhesion amount.

　（４）その他の工程
　ホットスタンプ用鋼板の製造においては、その他、酸洗、冷間圧延、調質圧延等、公知の製法を含んでもよい。 (4) Other processes In manufacturing the hot stamping steel sheet, other known manufacturing methods such as pickling, cold rolling, and temper rolling may be included.

　＜ホットスタンプ成形体の製造工程＞ <Manufacturing process of hot stamping body>

　本発明のホットスタンプ成形体は、ホットスタンプ用鋼鈑を、５００℃以上Ａ３点以下の温度域を１００℃／ｓ未満の平均加熱速度で加熱して保持した後、ホットスタンプ成形し、成形後、成形体を、室温まで冷却することにより製造する。 The hot stamping molded body of the present invention is a hot stamping steel sheet which is heated and held at a temperature range of 500 ° C. or higher and A3 point or lower at an average heating rate of less than 100 ° C./s, and then hot stamped and molded. The molded body is produced by cooling to room temperature.

　また、強度を調整するために、ホットスタンプ成形体の一部の領域又は全ての領域を２００℃以上、５００℃以下の温度で焼戻してもよい。 In order to adjust the strength, a part or all of the hot stamping body may be tempered at a temperature of 200 ° C. or higher and 500 ° C. or lower.

　５００℃以上Ａ３点以下の温度域を１００℃／ｓ未満の平均加熱速度で加熱することにより、ホットスタンプ用鋼鈑に生成した下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトの粒界がオーステナイトの逆変態サイトとして機能し、オーステナイトとマルテンサイトのテクスチャーメモリー効果によって、ホットスタンプ成形体において、下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界を８０％以上生成させることができる。 The lower bainite, martensite, and tempered martensite grain boundaries formed in the steel sheet for hot stamping are heated to a temperature range of 500 ° C. or more and A3 or less at an average heating rate of less than 100 ° C./s. It functions as a transformation site, and the texture angle effect of austenite and martensite allows the rotation angle to be 5 ° to 75 ° with the <011> direction of the crystal grains of the lower bainite, martensite, or tempered martensite as the rotation axis. Of the grain boundaries that are less than or equal to °, 80% or more of the grain boundaries that have a rotation angle of 15 ° or more can be generated.

　平均加熱速度が１００℃／s以上であると、微細炭化物がオーステナイトの逆変態サイトとなるため、オーステナイトとマルテンサイトのテクスチャーメモリー効果を得ることができない。好ましくは９０℃／ｓ以下である。下限は特に規定しないが、０．０１℃／ｓ未満であると、製造コストが不利になるため、０．０１℃／ｓを以上が好ましい。より好ましくは、１℃／ｓ以上である。 When the average heating rate is 100 ° C./s or more, fine carbides become austenite reverse transformation sites, so that the texture memory effect of austenite and martensite cannot be obtained. Preferably it is 90 degrees C / s or less. The lower limit is not particularly specified, but if it is less than 0.01 ° C./s, the production cost is disadvantageous, so 0.01 ° C./s or more is preferable. More preferably, it is 1 ° C./s or more.

　ホットスタンプ時の保持温度は、旧オーステナイト粒を微細化するために、Ａ３点＋１０℃以上、Ａ３点＋１５０℃以下とすることが好ましい。また、ホットスタンプ後の冷却速度は、強度向上の観点から１０℃／ｓ以上とすることが好ましい。 The holding temperature at the time of hot stamping is preferably A3 point + 10 ° C. or higher and A3 point + 150 ° C. or lower in order to refine the prior austenite grains. The cooling rate after hot stamping is preferably 10 ° C./s or more from the viewpoint of improving the strength.

　次に、本発明の実施例について説明するが、実施例での条件は、本発明の実施可能性及び効果を確認するために採用した一条件例であり、本発明は、この一条件例に限定されるものではない。本発明は、本発明の要旨を逸脱せず、本発明の目的を達成する限りにおいて、種々の条件を採用し得るものである。 Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

　表１－１～１－３に示す成分組成の溶鋼を鋳造して製造した鋼片に、表２－１～２－３に示す熱間圧延、冷間圧延を施してホットスタンプ用鋼板とし、該ホットスタンプ用鋼板に表３－１～３－３に示す熱処理を施して、ホットスタンプ成形を行い、成形体を製造した。 Steel strips produced by casting molten steel having the composition shown in Tables 1-1 to 1-3 are subjected to hot rolling and cold rolling shown in Tables 2-1 to 2-3 to obtain hot stamping steel plates. The steel sheet for hot stamping was subjected to the heat treatment shown in Tables 3-1 to 3-3, and hot stamping was performed to produce a molded body.

　表３－１～３－３に、ホットスタンプ成形体のミクロ組織と機械特性を示す。 Tables 3-1 to 3-3 show the microstructure and mechanical properties of the hot stamping products.

Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001

Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002

Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003

Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004

Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005

Figure JPOXMLDOC01-appb-T000006
Figure JPOXMLDOC01-appb-T000006

Figure JPOXMLDOC01-appb-T000007
Figure JPOXMLDOC01-appb-T000007

Figure JPOXMLDOC01-appb-T000008
Figure JPOXMLDOC01-appb-T000008

Figure JPOXMLDOC01-appb-T000009
Figure JPOXMLDOC01-appb-T000009

　ホットスタンプ成形体において、先述の方法により、下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトの面積率、下部ベイナイト又はマルテンサイト又は焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として回転角が５°以上７５°以下となる粒界のうち、回転角が１５°以上となる粒界の割合を測定した。 In the hot stamped molded body, the area ratio of the lower bainite, martensite, and tempered martensite, and the rotation angle of 5 as the rotation axis is the <011> direction of the crystal grains of the lower bainite, martensite, or tempered martensite. The ratio of the grain boundary where the rotation angle is 15 ° or more among the grain boundaries where the angle is from 75 ° to 75 ° was measured.

　ホットスタンプ成形体の強度は、引張試験を行い評価した。引張試験は、ＪＩＳ　Ｚ　２２０１に記載の５号試験片を作製し、ＪＩＳ　Ｚ　２２４１に記載の試験方法に従って実施し、最大強度が２０００ＭＰa以上を合格とした。 The strength of the hot stamped molded body was evaluated by a tensile test. For the tensile test, a No. 5 test piece described in JIS Z 2201 was prepared, and the test was performed according to the test method described in JIS Z 2241. The maximum strength was 2000 MPa or more.

　曲げ変形能の評価はドイツ自動車工業会で規定されたＶＤＡ基準（ＶＤＡ２３８－１００）に基づいて以下の測定条件で評価を行った。本発明では曲げ試験で得られる最大荷重時の変位をＶＤＡ基準で角度に変換し、最大曲げ角度を求め、最大曲げ角が５０°以上となった材料を合格とした。 The bending deformability was evaluated under the following measurement conditions based on the VDA standard (VDA238-100) defined by the German Automobile Manufacturers Association. In the present invention, the displacement at the maximum load obtained by a bending test is converted into an angle based on the VDA, the maximum bending angle is obtained, and a material having a maximum bending angle of 50 ° or more is regarded as acceptable.

　　試験片寸法：６０ｍｍ（圧延方向）×３０ｍｍ（圧延と垂直方向）、板厚１．０ｍｍ
　　曲げ稜線：圧延と直角な方向
　　試験方法：ロール支持、ポンチ押し込み
　　ロール径：φ３０ｍｍ
　　ポンチ形状：先端Ｒ＝０．４ｍｍ
　　ロール間距離：２.０×１．０（ｍｍ）＋０．５ｍｍ
　　押し込み速度：２０ｍｍ／ｍｉｎ
　　試験機：ＳＨＩＭＡＤＺＵ ＡＵＴＯＧＲＡＰＨ ２０ｋＮ Specimen size: 60 mm (rolling direction) × 30 mm (perpendicular to rolling), plate thickness 1.0 mm
Bending ridge line: direction perpendicular to rolling Test method: roll support, punch push-in roll diameter: φ30mm
Punch shape: Tip R = 0.4mm
Distance between rolls: 2.0 x 1.0 (mm) + 0.5 mm
Pushing speed: 20mm / min
Testing machine: SHIMADZU AUTOGRAPH 20kN

　本発明のホットスタンプ成形体は、引張強度が２０００ＭＰａ以上であり、優れた曲げ変形能を有することが確認できた。一方、化学組成、製造方法が適切でない例では、目標とする特性が得られなかった。 The hot stamped article of the present invention has a tensile strength of 2000 MPa or more and was confirmed to have excellent bending deformability. On the other hand, in the example where the chemical composition and the manufacturing method are not appropriate, the target characteristics were not obtained.

Claims (2)

　成分組成が、質量％で、
　　Ｃ　：０．３５％以上、０．７５％以下、
　　Ｓｉ：０．００５％以上、０．２５％以下、
　　Ｍｎ：０．５％以上、３．０％以下、
　　ｓｏｌ．Ａｌ：０．０００２％以上、３．０％以下、
　　Ｃｒ：０．０５％以上、１．００％以下、
　　Ｂ　：０．０００５％以上、０．０１０％以下、
　　Ｎｂ：０．０１％以上、０．１５％以下、
　　Ｍｏ：０．００５％以上、１．００％以下、
　　Ｔｉ：０％以上、０．１５％以下、
　　Ｎｉ：０％以上、３．００％以下、
　　Ｐ：０．１０％以下、
　　Ｓ：０．１０％以下、及び
　　Ｎ：０．０１０％以下を含有し、残部がＦｅ及び不可避的不純物であり、
　ミクロ組織が、下部ベイナイト、マルテンサイト、及び焼戻しマルテンサイトの少なくとも１種を、面積率で９０％以上含み、
　上記下部ベイナイト、上記マルテンサイト、及び上記焼戻しマルテンサイトの結晶粒の＜０１１＞方向を回転軸として、回転角が５°以上７５°以下となる粒界の長さに対する回転角が１５°以上となる粒界の長さの割合が８０％以上である
ことを特徴とするホットスタンプ成形体。 Ingredient composition is mass%,
C: 0.35% or more, 0.75% or less,
Si: 0.005% or more, 0.25% or less,
Mn: 0.5% or more, 3.0% or less,
sol. Al: 0.0002% or more, 3.0% or less,
Cr: 0.05% or more, 1.00% or less,
B: 0.0005% or more, 0.010% or less,
Nb: 0.01% or more, 0.15% or less,
Mo: 0.005% or more, 1.00% or less,
Ti: 0% or more, 0.15% or less,
Ni: 0% or more, 3.00% or less,
P: 0.10% or less,
S: 0.10% or less, and N: 0.010% or less, the balance being Fe and inevitable impurities,
The microstructure contains at least one of lower bainite, martensite, and tempered martensite in an area ratio of 90% or more,
With the <011> direction of the crystal grains of the lower bainite, the martensite, and the tempered martensite as the rotation axis, the rotation angle with respect to the grain boundary length at which the rotation angle is 5 ° or more and 75 ° or less is 15 ° or more. A hot stamping molded product, wherein the ratio of the length of the grain boundary is 80% or more. 　めっき層を有することを特徴とする請求項１に記載のホットスタンプ成形体。 The hot stamping body according to claim 1, further comprising a plating layer.
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EP3778951B1 (en) 2024-08-28
JPWO2019186930A1 (en) 2020-04-30
CN111655885A (en) 2020-09-11
EP3778951A1 (en) 2021-02-17
EP3778951A4 (en) 2021-10-27
US20210010118A1 (en) 2021-01-14

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